Bathing appliances in the nature of spas, or so-called hot tubs, have become commercially successful. These spas are typically constructed as a molded shell to form a water containment, with seats, footwells, platforms for reclining, and the like molded into the shape of the shell. The shell is usually molded from plastic or fiberglass or a composite thereof. A pump or pumps usually placed in a chamber under the shell draw water from the water containment and reinject the water, usually with air, into the containment through a variety of nozzles, hydrotherapy jets, and the like. The jets are usually mounted in the shell under the water line, and are designed to provide a comforting or therapeutic effect to a person in the spa. The jets are usually mounted by making a hole in the shell, and fixing the jet in the hole by a use of seals, adhesives, welding compounds, or a combination thereof. Water supply lines from the pumps to the jets are usually flexible tubing or rigid PVC tubing. After the jets and tubing are in place, an expandable foaming polymeric material is blown into the empty spaces to provide thermal and sound insulation. This construction system has been used widely and successfully, and is currently almost universally used.
One of the problems of conventional spa construction is that the configuration of the spa is essentially fixed at the time of construction. Since the jets are fixed in a hole in the spa shell, replacement of the jet is difficult or impractical. Replacement in the least would required an extensive reconstruction involving removing the old jet (usually by cutting out the jet), and installation of the new jet requiring repair and resealing of the shell around the new jet. In addition, the water and air supply lines to the jets must be replaced or reinstalled on the new jet, requiring access from the bottom of the spa and removal and replacement of the foam insulation surrounding the lines. Because such replacement is burdensome, a user will usually avoid a jet replacement unless absolutely necessary. If a new jet type is introduced into the market or the tastes of the bather change for a difference jet type, the difficulties of replacement basically preclude user from changing the jets.
Another problem involving jet replacement is that the water supply systems or jets are usually buried in insulating foam under the spa shell. If a jet is replaced with a different type that requires a different water flow, the function of the remaining jets attached to the same pump can be compromised as the pressure drops or rises due the increased or decrease flow through the new jet. It may be possible to solve the problem by installing a pump of a different capacity, or by rearranging the water supply lines between different pumps in the spa to redistribute the water flow between the pumps. However, both alternatives are expensive, and the later involves extensive labor in digging out the old piping and reinstalling the new.